1. Technical Field
The present invention relates to a device for illuminating the license plate (information plate) of a car and more particularly to an illuminating device using an LED (a light emitting diode) for a light source.
2. Background Art
As a device for illuminating a license plate, a related art incandescent bulb has been used for a light source as in JP-A-2000-168438. However, the incandescent bulb has a problem in that its lifetime is short and a great deal of time and labor is required to change the bulb due to a burnout. Furthermore, the amount of consumed power is great, the burden of an on-board battery is heavy, and an installation space is large, and the degree of freedom of the design around the license plate is low. Therefore, use of the LED for the light source has been investigated. Since the LED has a long lifetime, a small size and small power consumption, it is possible to effectively solve the foregoing related art problems of the incandescent bulb.
When the LED is provided on one of the sides of the license plate and a light is irradiated from the LED toward the surface of the license plate to carry out an illumination process, the surface of a close region to the LED can be illuminated to be brighter, and the surface of a region further away from the LED is less illuminated to be darker.
Similarly, a technique using the incandescent bulb in JP-A-2000-168438 has such a problem. For this reason, JP-A-2000-168438 discloses evenly illuminating almost the whole surface of the license plate by providing a diffusion lens step region in a lens to diffuse a light. However, the LED has a high directivity of an emitted light and the surface of a region provided along an optical axis is bright, and the surface of a region away from the optical axis is dark.
Even if the diffusion lens step is simply provided as in JP-A-2000-168438, it is impossible to solve the problem of the nonuniform brightness. Thus, there is a problem in that it is hard to uniformly illuminate the surface of the license plate by the LED.
Moreover, a plurality of LEDs can be provided around the license plate to uniformly illuminate the surface. However, the number of the LEDs is increased so that a cost is increased. Furthermore, it is impossible to avoid the undesired external exposure of the LED provided around the outside of the license plate. As a result, there is another problem in that an outer appearance is deteriorated.